Rotatable surface conditioning rolls ("mill rolls") are commonly used in the manufacture and processing of metal sheets or metal coils in continuous production lines. Such surface conditioning rolls are generally utilized in so-called "wringer applications" as well as "oiler applications".
In wringer applications, mill rolls and like articles are used to prevent the cross contamination of treating solutions. For example, the manufacture of metal coil or strip typically involves many process operations using a variety of treating solutions designed to variously clean, degrease, remove scale, pickle, rinse, surface etch, lubricate, and/or protect the metal surface. During these operations, it is important to prevent the contamination of these often incompatible treating solutions. Thus, a squeegeeing ("damming") operation is performed at the surface of the metal sheet to remove excess treating solution from the metal surface as the metal strip exits each of the treatment tanks to thereby prevent the inadvertent mixing of treating solutions. Squeegee arrangements have included the use of conventional rotatable rubber rolls as well as wiper bars made of felt or cork. These prior rolls or wiper bars, however, have generally suffered relatively short useful lives in the aforementioned wringing applications.
In oiler applications, materials ("oils") are applied to the surface of metal sheets or foils as protection against corrosion, to prevent handling marks or to provide lubrication for subsequent processing steps. Control of coating thickness is desired in such oiler applications in order to optimize the procedure by using the minimum amount of material needed in the application. The use of rubber rolls in these applications has been unsatisfactory because of their relatively short useful lives.
The short lives of the rubber rolls in the foregoing applications is attributable to the structural properties of the rubber surfaces including, for instance, their non-compressibility. The relatively non-compressible nature of rubber rolls, for example, makes them susceptible to cut propagation and other structural damage at the nip of the roll. Additionally, the surfaces of rubber rolls are easily torn, gouged or cut by the edges of the splices in the metal sheet. Once a rubber roll has been damaged, the initial cut, tear, or gouge will usually enlarge due to compressive forces at the nip and tension forces on either side of the nip. Consequently, frequent repair (e.g., surface dressing) or replacement of these articles has been required, thereby creating unscheduled production line downtimes with associated losses and costs.
Moreover, the closed, non-porous nature of the rubber surfaces of the foregoing rolls, renders repair quite onerous, if possible at all. For example, repair splices and patches applied to a damaged rubber roll can present a surface incongruity that may damage the metal sheets being manufactured or otherwise treated. Finally, the aforementioned rubber are known to hydroplane when wet, thereby undesirably disrupting the contact between the roll and the metal sheet.
To address the above mentioned drawbacks associated with the use of rubber surface conditioning products, rolls and bars made of compacted, unified, discrete sheets of nonwoven fabric have been used in the foregoing applications. In general, nonwoven fabric articles have been stronger and more resistant to tears and cuts than rubber rolls, for example. Moreover, nonwoven fabric articles possess the ability to self heal, thereby helping to minimize the risk of production line shutdown due to roll (or bar) failure. The porous nature and high void volume inherent in these nonwoven fabric articles provide a high degree of absorbency to aid in squeegee and tension applications. In addition, the absorbency of the fabric articles is useful in applying thin uniform film thicknesses of lubricants or other solutions onto metal sheet surfaces in oiling applications.
The porous surfaces of nonwoven fabric articles permit loose debris (e.g., fine metal particles or dirt) to be picked-up from the surface of metal sheet, or the like. The debris penetrates into and is retained within the body of the article, thus preventing the debris from scratching or causing coil marks on the metal sheet material. Nonwoven fabric articles also provide a high coefficient of friction on many metal surfaces and they stay in contact with metal when wet to maintain the uniform high tension needed to prevent significant slippage.
Although fabric articles generally have enjoyed longer useful lives than their rubber counterparts, fabric articles are known to be susceptible to damage when exposed to very harsh chemicals such as strong acids, caustic liquids, electro-plating solutions and the like. In the manufacture of metal sheeting, for example, a variety of harsh chemical agents are typically used. Treating agents containing relatively high concentrations of hydrochloric acid, sulfuric acid, chromic acid, salts of the foregoing acids or basic agents such as sodium or potassium hydroxide are commonly used. Solutions of these treating agents can have a pH less than one or as high as 14. After a treating agent has interacted with the surface of the metal sheet, two squeegeeing operations coupled with water rinsing are generally required to effectively remove the agent from the metal surface. Many of the organic polymeric materials used in the manufacture of the foregoing nonwoven fabric articles will degrade or disintegrate after repeated squeegee operations which expose the article to treating solutions at the extreme pH values mentioned above. In particular, the exposure of such articles to extreme caustic conditions (e.g., pH of about 14) in the presence of oils is known to readily degrade nonwoven fabric articles.
Fabric articles are described in the technical and patent literature, as discussed below. Other than the surface treating article described by Lux et al. (U.S. Pat. No. 4,669,163), none of the cited references discloses a surface conditioning article having a desired resistance to harsh chemical environments.
Kusters (U.S. Pat. No. 2,801,461) discloses a roll for use in squeezing liquids from textiles made of a plurality of flat, angular, axially compressed discs composed of nonwoven fibers bonded with vulcanized latex. The discs are mounted and retained under compression on a support shaft. The fibers uses in the described article include tensilized nylon and natural fibers such as ramie, cotton, or sisal-hemp.
Kai (U.S. Pat. No. 3,853,677) discloses a roll made from axially compressed discs of a nonwoven fabric formed from a mixture of natural fibers and fibers made from a high molecular weight synthetic polymer wherein the fibers are bonded with a resinous material. The discs are heated and compressed at 78.times.10.sup.6 Pa to form a finished roll having a Poisson's ratio of about 0.5 and shearing stress of about 1200 kg/m.sup.2.
L. W. Legacy, in "Recent Advances in Wringer Roll Technology", Iron and Steel Engineer, Vol. 60, No. 4, April, 1983, pp. 42-44, discloses the preparation of rolls made of compacted discs of nylon staple fibers bonded with a strong flexible binder resin. Legacy describes these rolls as more tear and cut resistant than conventional rubber covered rolls and capable of self-healing after exposure to large local stresses. The described rolls, however rolls may not be used in applications exposing them to a pH outside the range of 2 to 10. Below a pH of 2, the fibers in the articles dissolve, and above a pH of 10, the resin that binds the fibers together dissolves.
Lux et al. (U.S. Pat. No. 4,669,163) disclose a polyolefin fiber wringer roll compressed and bonded in a specified manner and made with heat-activated binder fibers to provide an article resistant to acidic and alkaline environments. The use of an organic solvent-borne acrylonitrile-butadiene copolymer as an optional fiber binder is disclosed. Although the article described by Lux et al. represents an advance in the art, there continues to be a need for better-performing, longer lived squeegee articles, especially for use in highly-alkaline environments and in the presence of oils.
Watanabe (U.S. Pat. No. 4,368,568) discloses a rubber covered roll comprising roughened metal core and a polyurethane covering with an intermediate layer consisting of a spirally-wrapped inorganic fiber layer (adjacent the metal core) and an organic fiber layer, both layers containing inorganic powder and a thermosetting resin.
Edwards (U.S. Pat. No. 4,475,275) disclose a method for producing a filled calendar roll by a stacked-disc manufacturing method employing vacuum compression.
Ocker et al. (U.S. Pat. No. 4,583,966) disclose a stacked-disc manufacturing method employing vibratory compression.
Takeda et al. (U.S. Pat. No. 4,400,418) disclose a dampener roll with a woven fabric covering comprising, in part, polyurethane fibers or yarns.
German patent reference 2,632,848 (MSKD) discloses stacked rubber discs bonded by harder rubber and the product is useful for squeegee applications.
Japanese patent reference 2-046310 (Hisayuki) discloses a hollow-fiber roll.
Fish (U.S. Pat. No. 1,854,509) discloses a filling for a calendar roll having heat resistant sections which can be formed of laminated discs made of heat resistant material.
French Patent Application No. 78 22829 discloses a hard felt roll formed by the compression of numerous hard felt, resin-impregnated disks on a steel mandrel to form a roll. The resin can be a butadiene resin, such as a butadiene-acrylonitrile rubber and a butadiene-styrene rubber, among others disclosed.
Degarabedian et al. (U.S. Pat. No. 4,603,075) disclose a composite shoe component comprising a polyester nonwoven fabric layer needle-punched to a woven polypropylene scrim, with the resulting combination being saturated with acrylonitrile butadiene styrene resin having a Tg of -10 to -40.degree. C. with specified tear strength and permeability.
Brafford (U.S. Pat. No. 3,800,381) discloses a covered roll for paper making having an outer cover formed of a wet lay process with a reinforcing mat of nonwoven needled polyester fibers which are wetted and impregnated with a binder material at room temperature and placed on the outer surface of the roll.
Fukuyama et al. (U.S. Pat. No. 3,490,119) disclose a polyurethane rubber covered roll for textile, paper and metal industry usage where the rubber is coated over a metal core reinforced by resin-impregnated fiber.
McGaughey et al. (U.S. Pat. No. 3,646,651) disclose an abrasion and corrosion resistant composite structural material, specifically rolls for use in steel-fabricating processes, where the roll is formed with variegated layers including fibrous reinforcing materials and an outermost resilient covering described as rubber material.
Curtis et al. (U.S. Pat. No. 5,247,740) disclose a method for forming a longitudinally extending keyway portion in a mill roll having a central bore.
It can be appreciated that further refinements and advances in the important technology embodied by nonwoven fabric articles should be of interest and value to the milling industry. It is desirable to fulfill a long felt and unsolved need by providing nonwoven fabric articles such as mill rolls or the like useful in surface treating applications which provide the aforementioned advantages of prior nonwoven fabric articles while also being chemically resistant. It is especially desirable to provide such articles having a construction suited for use in harsh chemical environments wherein the articles are exposed to extremely acidic or extremely caustic solutions, and especially caustic solutions in the presence of oils. It is also desirable to provide a method for the manufacture of the foregoing articles.